Piping networks for conveying fluids (liquids, gases, powders, slurries, sludges and the like) are used in a wide spectrum of industries including the petroleum industry, the chemical industry, mining, construction, manufacturing, as well as in municipal water service. It is advantageous to assemble piping networks using pipe segments sealingly joined to one another with mechanical fittings. Mechanical fittings typically comprise couplings that engage the pipe ends and are held together by removable fasteners.
Mechanical fittings are advantageous because they avoid the use of open flame or electrical arc, as required in welding, to effect a fluid tight joint between pipe ends. The assembly of mechanical fittings requires less skill than welded or brazed joints, and they are, therefore, less expensive to fabricate. Mechanical fittings also provide greater versatility for modification or repair of the piping network since repairs can be effected or new sections can be added by simply unbolting existing couplings and making the new connections as desired.
A problem common to all piping networks, regardless of how the pipes are connected, is the lack of joint flexibility axially (lengthwise along the pipe), torsionally (rotation about the long axis of the pipe) and angularly (the relative angle between one pipe and another to which it is connected). Rigid joints mean that the tolerances to which the pipes are cut and the angles at which they are joined must be maintained within relatively close limits so that the piping network will fit together as designed, without significant deviation from the plan. It is expensive and not always possible to maintain the necessary tight tolerances on pipe lengths, especially when the networks are assembled in the field as opposed to in a workshop where conditions for cutting and assembly are under greater control.
Flexible pipe joints are also advantageous for piping networks that must expand or contract and yet maintain fluid-tight connections. In one example, a piping network for the pneumatic transport of pulverized coal from the coal crushing station to the furnace in a power plant must have enough flexibility to maintain its connection to the furnace, which expands in size when in operation due to the heat generated when the coal is burned.
Furthermore, pipes in a chemical plant or refinery, for example, that carry fluids that are hotter or colder than ambient conditions, are subject to cycles of heating and cooling, and the associated changes in length that such cycles occasion. These piping networks typically require multiple expansion joints or loops to avoid over-stressing the pipes due to expansion and contraction, especially for long pipe runs. Pipes joined by flexible couplings readily accommodate the deflections due to thermal expansion and contraction and thereby eliminate the need for special expansion joints or loops in the network.
Piping networks may also be subject to significant motion, for example, when built over seismically active regions of the earth. Deflections of pipes during tremors and minor earthquakes may be accommodated by flexible couplings that maintain the fluid integrity of the joints.
There is clearly a need for pipe couplings which provide a degree of flexibility to the joints of a piping network that will enable the network to be assembled in the field, according to design, without maintaining close tolerances or the need for modifications that deviate from the plan substantially, and accommodate thermal expansion and contraction as well as other deflections without compromising the integrity of the joints.